#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include <string.h>

int main() {
    const char* str = "Hello, world!";
    const char* substr = "world";

    const char* found = strstr(str, substr);
    if (found != NULL) {
        printf("Substring found at index: %d\n", found - str);
    }
    else {
        printf("Substring not found.\n");
    }

    return 0;
}